This invention relates to concrete admixtures. In one particular aspect it relates to concrete admixtures for use as cold weather concrete set accelerators, and to methods for their use.
Low or freezing temperatures ( e.g., 40.degree. to 15.degree. F.) presents special problems in mixing, placing and curing of concrete. Concrete may freeze while saturated and subsequently be of low strength, or there may be a slow development of strength.
The American Concrete Institute (ACI) Report 306R-78 on Cold Weather Concreting, sets forth standard practices to prevent freezing, and assure the safe development of concrete strength during curing at ambient freezing conditions. Heating of materials, including mix water and aggregates, are mandatory. Protective insulating coverings, heating enclosures and proper curing conditions are described.
An additional factor (not often reported) associated with freezing temperatures, is the distress of the concrete worker operating under adverse conditions. Even if dressed warmly, the concrete worker wishes to finish a pour or complete the finishing as fast as possible, and move indoors out of the wind and cold. Thus, an accelerated set time is an important aspect of cold weather concreting.
While the prior art has addressed the problems of using concrete in cold weather (e.g., the use of calcium chloride as the principle accelerating admixture), it has not successfully developed admixtures which are, (1) non-corrosive, and (2) meet or exceed the rate-of-hardening and compressive strength performance at about 13.degree. to 40.degree. F., of a plain concrete mix at 50.degree. F.
The present invention provides admixture compositions which meet these prior art limitations.